1. Field of the Invention
The invention involves a process for preparing a matte, photosensitive silver halide recording material in which the particles of the matting agent are photosensitive and are darkened when an image is recorded.
2. Description of Related Art
Photosensitive silver halide recording materials frequently have a matte surface. The surface roughness diminishes the tendency to accumulate an electrostatic charge and the susceptibility to scratches by coarse dust particles. The roughness also facilitates removing air between the original and the recording material in reprographic copying.
The most important method for producing surface roughness practically is to add finely divided solid materials to coating solutions.
If the layer containing the particles of the solid material is coated simultaneously with the silver halide emulsion layer on the same side of the support and dried, the undesirable "starry night" effect can occur. In this case, exposed and processed image areas show pinpoint light spots. These are caused by particularly large particles or agglomerates of the usually polydispersed, finely divided solid material, which, on drying, displace the silver halide emulsion laterally.
DE 37 00 551-C2 describes a photosensitive silver halide recording material containing a photosensitive matting agent of 1 to 30 .mu.m particles. These darken after exposure and processing and therefore, do not cause light spots if the particles displace the silver halide emulsion. The particles of this matting agent contain a chemically and optionally, spectrally, sensitized silver halide, a binder, and a finely divided solid with a particle size clearly below that of the matting agent and with no permanent inherent color.
The preparation of photosensitive matting agents described in the current art requires several operating steps. In the simplest instance, a portion of the silver halide emulsion intended for the photosensitive layer of the recording material is mixed with a hardening agent and the finely divided solid, and is spray-dried. The resulting powder is screened, if necessary, and added to one of the coating solutions in preparing the photosensitive material. Obviously, these process steps, which are somewhat unusual for the photographic products industry, must be conducted under darkroom conditions.